The effect of completion ID in four different sand control completions was studied using inflow modeling and reservoir simulation. An expandable sand screen and three different IDs of external gravel packs were studied, in various lengths of horizontal well and over a range of flow rates.
The ID of a completion affects the performance of a completion through the flow friction pressure generated. The friction pressure is a function of the ID to the inverse 5th power so even small changes in ID can have an effect.
Each completion configuration was assumed to have the same realistic production rate. The friction pressure tends to act as a choke on production from the toe of the well; this concentrates production towards the heel. The expandable sand screen has the lowest inflow at the heel and the smallest ID gravel pack has the highest inflow. The high inflow at the heel draws water up from the underlying aquifer and initiates water breakthrough. The time to breakthrough was calculated using a simple analytical theory. The predicted time agreed well with available production data.
A reservoir model was built to further study the heterogeneous inflow. This showed that the larger ID completions gave the best sweep of the reservoir with the highest recovery. The reservoir model was run for a variety of well lengths and productions rates and showed that for long high rate wells the completion with the largest ID gave the best sweep and the longest water breakthrough time.
Long horizontal wells are an increasingly common option for the drainage of certain reservoirs. They have numerous advantages over vertical wells. Larger contact with the formations gives low flow rates and drawdowns. This is especially valuable in wells drilled close to the oil water or gas il contact, such as in oil rim or attic developments. It is crucial in the planning of such developments that the effects of wellbore friction are taken into account. In a horizontal well of infinite hydraulic conductivity the friction is zero and the drawdown and inflow are constant along the entire well length. For a finite hydraulic conductivity the friction pressure causes variations in drawdown and inflow along the well.
The effect of friction in a horizontal well is to concentrate production towards the heel of the well. This is due to flow from the toe experiencing an additional backpressure due to the friction, which inhibits inflow. The high flow at the heel, which can be double the infinite conductivity case, accelerates water or gas coning into the well. There are ways to deal with this effect, both before and after the fact. For long drains, inflow control devices can be placed in the screens to choke back the flow at the heel. This in effect chokes back production and it is still difficult to achieve the correct inflow without downhole flow and pressure measurements. After water breakthrough, options involve downhole flow control and water shut off treatments.
